The present invention relates to a spectrophotometer, such as an ultraviolet visible spectrophotometer, infrared spectrophotometer, and fluorescence spectrophotometer, for analyzing light from a sample onto or into which a beam of light is delivered. More precisely, it relates to a spectrophotometer capable of setting at will the wavelength of light to be delivered onto a sample or the wavelength of light from the sample by driving a wavelength dispersion element.
Generally, a fluorescence spectrophotometer includes: an excitation spectroscopy system for separating light of a predetermined wavelength from the light emitted from a light source and for delivering the light as an excitation light to a sample; a fluorescence spectroscopy system for separating light of a predetermined wavelength from the fluorescence emitted from the sample in response to the excitation light; and a fluorescence detector for detecting the light separated by the fluorescence spectroscopy system and for providing a signal (which will be called “a fluorescence signal” hereinafter) corresponding to the amount of the light detected. The fluorescence signal provided from the fluorescence detector is converted from analog to digital form (i.e. A/D converted), and after that it is computed in a data processor to perform a qualitative/quantitative analysis of the sample.
The excitation spectroscopy system and fluorescence spectroscopy system each include a wavelength dispersion element such as a diffraction grating or prism, and a driving unit for rotationally driving the wavelength dispersion element. The direction of the wavelength dispersion element with respect to the incident light can be appropriately changed by the driving unit so that the wavelength of the excitation light and that of the light detected by the fluorescence detector will be set at will (for example, see Patent Document 1).
In such a fluorescence spectrophotometer, immediately after the wavelength dispersion element is rotated by the driving unit and stopped at a predetermined position, the fluorescence signal is not stabilized since the wavelength dispersion element vibrates. If a qualitative/quantitative analysis on a sample is performed with an unstable fluorescence signal, a correct analysis result cannot be obtained. Given this factor, in a conventional fluorescence spectrophotometer, a period of time in which the diffraction grating's vibration will most likely converge is previously set, and the fluorescence signal after the period of time has elapsed is used for the analysis. However, given the variation between apparatuses, the period of time for the vibration to converge has to be set rather long, which prolongs the waiting time from the initiation of the diffraction grating's driving to the initiation of the measurement.
Generally, fluorescence signals from a fluorescence detector are A/D converted at predetermined sampling intervals and then are sent to a signal processor. In the signal processor, a predetermined computational processing and electrical noise removal processing using a plurality of digital signals are performed, and the result is provided to an output unit such as a display and printer. Hence, the larger the number of signals sent to the signal processor is, the more the analysis accuracy improves. However, in the method in which a measurement is initiated after waiting for the convergence of the diffraction grating's vibration, the number of obtainable pieces of data is small.
One method for avoiding this problem is to initiate a measurement before the vibration of the diffraction grating converges and perform computations or other processes to reduce the influence of the vibration generated in the diffraction grating. With this method, however, it is difficult to completely eliminate the influence of the vibration although the number of obtainable pieces of data can be increased.
Alternatively, a sensor for detecting the vibration of a diffraction grating may be provided and the data-collecting operation may be started as soon as the convergence of the diffraction grating's vibration is detected. With this method, the waiting time for the initiation of measurement can be shortened as much as possible and the number of pieces of sampling data can be increased. However, the product cost increases for providing the vibration detection sensor.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-83093 ([0010], FIG. 1)